1. Field of the Invention
The invention relates to a metallurgical vessel for melting device or holding devices for liquid metal. It comprises a top part as well as a bottom part provided with a collar on which the top part is supported. The bottom part receives the melt and, above the melting zone, the slag zone adjoins as an area of the generated slag. At the level of the slag zone, an annular cooling device is arranged between the vessel top part and the vessel bottom part.
2. Description of the Related Art
Melting vessels, for example, electric arc furnaces operated with direct current or alternating current are known in the prior art. They are comprised of a water-cooled top part and a refractory-lined bottom part. The bottom part is comprised of a metal jacket or sheet metal plates that are not cooled. The sheet metal jacket has, for example, a collar on which the top part is supported. The bottom part extends across the melting zone as well as the slag zone.
These bottom parts, in particular in the area of the slag zone, are exposed increasingly to thermal stress. This is so, on the one hand, because of the furnace operation that entails ever increasing melting output and shorter intervals between tapping. On the other hand, refractory materials and refractory material qualities having a high carbon contents are used that lead to an improved thermal conduction from the interior of the furnace to the furnace vessel. In this way, the thermal loadability of the sheet metal plates of the furnace jacket or vessel bottom that are not cooled is often surpassed. The result of such local overheating of the bottom part in the area of the slag zone is warping or deformations of the vessel to the point of necessitating a replacement of the sheet metal jacket.
Moreover, the occurring deformations make it more difficult to line the vessel with refractory material and affect the service life of the refractory material.
Since the top part is supported on the bottom part, deformations of the top part may also result as a subsequent damage in the case of excessive deformations of the bottom part.
Such a furnace vessel with top part and bottom part is disclosed in European patent 0 699 885 B1. The bottom part is comprised of a jacket of sheet steel having a collar wherein the bottom part is lined with refractory material. In order to minimize heat loss that results from the fact that the entire vessel wall area is cooled, it is proposed that the vessel wall is cooled only by an upper and a lower cooling device and the intermediately positioned area of the vessel wall above the slag line that faces the interior of the vessel is comprised essentially of refractory material. The second lower cooling device in the form of a ring is arranged at the level of the slag line. The top part of the vessel rests on the refractory lining of the bottom part as well as on the collar of the sheet metal jacket. In addition to providing the cooling function, the second lower cooling device at the same time provides also the supporting structure for the ceramic wall part and the lid of the furnace vessel. The top part of the vessel is supported by means of an exterior cage that extends about the entire top part of the vessel.